With both Ethernet and IP powering Data Center Networks (DCNs), one should wonder if their coexistence is necessary or an unquestioned legacy. Especially in cloud DCNs, the role of layer-2 is diminishing rapidly as the vast majority of applications only require layer-3 connectivity. At the same time, cloud workloads are demanding that DCN architectures better support network scalability, multitenancy, address virtualization, and end-host mobility. This paper argues that today’s DCN architectures have a conjoined layer-2 and layer-3 design that is not only unnecessary, but is counter productive. We present AIN, a blueprint for scalable all-IP DCN. AIN implements virtual routers inside hypervisors, eliminating the need for virtual switching. It leverages the proven scalability of routing protocols and avoids unnecessary packet encapsulation, while supporting both multitenancy and end-host mobility. Finally, AIN is compatible with existing applications and is fully realizable with current protocols and hardware.